In a typical cheese-making operation, milk is inoculated with an appropriate culture often called a starting culture or bacterial starter. The bacterial starter causes acidity to develop in the cheese as a result of lactic acid formation. The various bacterial additions also produce various cheese types. Thereafter the thus inoculated milk is contacted by stirring with an appropriate amount of enzyme rennet used to coagulate the casein in the milk to produce the cheese curds. While coagulation takes place, the vessel contents are not stirred. This batch reaction may be conducted in another tank although the same tank may be utilized. Thereafter stirring is resumed; curd formation takes place, and whey is separated from the curds. Thereafter a salt wash may be used to separate further the whey from the cheese. Whey, of course, is not affected by rennet.
Typically the feedstock is at a proper pH, e.g. about 6-6.5, and temperature and thus produces the controlled quality of cheese sought to be obtained. The present invention, however, does not relate to acid precipitation such as at a pH of 4 to 5, e.g. for cottage cheese.
As it is evident from the above description, cheese-making is essentially a batch process wherein different vessels may also be used to produce different reactions. These operations are described in literature such as Van Slyke and Price, "Cheese", Orange Judd Pub. Co., New York, NY (1949).
In an endeavor to reduce the large scale batch vessels or to speed up the production of cheese, a number of batch or semi-batch operations have been proposed.
One of the proposed methods requires an enzyme deposited on flat surfaces. The substrate, that is the bacterially inoculated material, is flowed past the enzyme. Thus the substrate is being treated in a continuous manner.
These surface deposited enzymes, of course, have imposed a great limitation on the flow rates, especially since the enzyme deposition has been by adsorption on a surface when these enzymes have been sought to be deposited on the surface.
Additionally, long pipe reactors have been proposed such as where rennet and milk are mixed in the pipe reactor, and then dumped in a vessel, or a long pipe reactor for a flow method in which the reaction would take place on the walls of the pipe containing the adsorbed enzymes.
According to the last method the bacterially inoculated material flows through the pipes at low velocities so as not to strip, by turbulent flow, the enzymes deposited on the wall surfaces. As it is well known, at low velocities the laminar flow conditions obtain and the velocity profile in a pipe reactor often resembles substantially a parabola. As the reaction rates are different based on the velocity profile as well as the turbulence or lack thereof, the production quality or yield often suffered.
Additionally, various enzymes deposited on filter surfaces likewise have been sought to be immobilized by other enzyme carriers which were retained on the filter material, e.g. due to mesh constraints or filter material type for filter leaves of the apparatus. The fluid flow had been sought to be such as to cause the reaction to be continuously conducted.
However, one of the great shortcomings of the prior art batch, wall, or leaf filter type of reactors has been the inexact rennet to milk ratio caused by improper mixing, or clogging and/or stripping of these surface-deposited materials which all have affected the fairly sensitive rennet to milk ratios, thus adversely affecting the necessary quality, control and yields.
Moreover, only a substrate of a high degree of purity could be employed to produce the desired or sought-after enzymatic conversion at sacrifices in reaction rates and flow rates. As a general proposition, all substrate materials which carried particulates such as proteins, fats, coagulants, etc., would cause to blind, i.e. clog, the reaction surfaces. Moreover, these particulates will also cause to strip the enzyme from the reaction surfaces. Hence, substantially non-uniform, noncontrollable reactions would occur. As a result, only partially reacted products could be obtained which then thereafter had to be further treated or mixed to be normalized as to content, quality, etc., to obtain the sought-after product.
In order to remove the disadvantages of enzyme stripping and low flow rates, various other approaches have been used such as pulsating reactors which supposedly attempt to overcome the disadvantages of the prior art apparatus limitations, yet rely on the batch process advantages of quiescent coagulation followed by pulsation.
Other attempts have been made to fluidize a reaction using fluid bed principles. For example, the enzyme is deposited on the fluidized heterogeneous phase with a substrate forming the liquid phase being reacted upon by the fluidized particles. As it is known from fluid bed mechanics, considerable abrasion exists between the fluidized particles which results in the loss of enzyme. Thus fixed and fluid bed reactors have been suggested with various attempts made to improve the mass transfer, the rates and/or interface restrictions in the prior art reactors or processes.
Needless to say, these complications have introduced numerous problems such that the continuous cheese-making process has been a long sought-after goal. Hence the present process has as an objective the production of cheese at substantially improved rates, with high quality, in a consistent and controlled manner at either low or high temperatures, with a tolerance for a high percentage of particulates in the substrate, excellent rennet to milk ratios, repeatable, controlled precise exposure to rennet, with substantial elimination of operator error, and also if desired a cheese without rennet being present.